NMR study of the unfolding of ribonuclease A, and dynamical studies of liquids in confined geometries
Zhang, Jing
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https://hdl.handle.net/2142/23529
Description
Title
NMR study of the unfolding of ribonuclease A, and dynamical studies of liquids in confined geometries
Author(s)
Zhang, Jing
Issue Date
1994
Doctoral Committee Chair(s)
Jonas, Jiri
Department of Study
Chemistry, Physical
Discipline
Chemistry, Physical
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
The cold, heat, and pressure unfolding of RNase A has been studied by 1D and 2D $\sp1$H NMR spectroscopy, spin-lattice relaxation time measurements, and the pressure-jump hydrogen-exchange method. It was found that the pressure denatured states of RNase A display some characteristics of a molten globule, and all three $\alpha$-helices and the $\beta$-sheet of the native protein remain partially folded structures in the pressure denatured state. $\sp1$H spectra of the denatured RNase A suggest that the cold and pressure denatured states are more structured than the heat denatured state, while the cold denatured state is more structured than the pressure denatured state.
The second part of this thesis contains several studies of liquids in confined geometries. These studies show that the motional behavior of a fluid confined to a region approaching molecular dimensions can vary dramatically with the degree of confinement. NMR study of the geometric confinement effects on the anisotropic rotational diffusion of acetonitrile-d$\sb3$ indicated that confinement of liquid acetonitrile to porous silica glasses increases its motional anisotropy. In the high resolution and high pressure $\sp{13}$C NMR study of model liquid lubricant 2-ethylhexyl benzoate confined to porous silica glasses, the comparison of the spin-lattice relaxation rates of the surface liquid (1/T$\rm\sb{1S})$ for each carbon with the 1/T$\sb1$ values for individual carbons in bulk EHB provides information on motional dynamics of EHB at the liquid/surface interface. The experimental $\sp{13}$C spin-spin relaxation rates (1/T$\sb{2})$ obey a 1/R$\sp2$ dependence for confined EHB, confirming that at low frequency the pure geometric confinement effects dominate over surface interaction effects. By analyzing the relaxation of the confined EHB under high pressure in terms of a model assuming a Cole-Davidson distribution of correlation times, it was found that the geometric confinement dramatically enhances the anisotropic reorientation of EHB, and the width broadening of the correlation time distribution originates from the surface. The study on the glass transition of liquids confined to porous silica glasses shows that for all liquids studied in the experiment the confinement lowered the T$\rm\sb{g}$ observed. The relative temperature depression of the liquid-glass transition ($\rm\Delta T/T\sb{g})$ due to confinement was found to be much smaller than that observed for freezing point depression.
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